You'll update every setting related to movement in your settings for all axes, update position settings for the offsets/softlimits/et. Just converting everthing by the mm to inch conversion.
speeds/velocities: divide by 25.4
steps per unit: multiply by 25.4 (multiplying because the units is in denominator...)
accel rates: divide by 25.4.
etc, etc, all axes, all settings related.
Attached may help, start you off.
The attached may not be all encompassing of your machine, if you have tool changer positions, etc, you'll have to convert them all as well.
regards
Eric